Japanese Patent Laying-Open No. 8-126121 discloses a charging apparatus mounted on an electric vehicle. The charging apparatus mounted on a vehicle includes two permanent magnet motors, two inverters provided corresponding to respective motors, a battery, a connecting circuit connecting a commercial power supply to a neutral point of each motor, and a control circuit charging the battery from the commercial power supply by causing equal currents to three-phase coils of the motors.
In the charging apparatus mounted on a vehicle, equal currents are caused to flow through three-phase coils of the motors and, therefore, generated magnetic fields are cancelled out by each other to be zero. Therefore, by the charging apparatus mounted on a vehicle, it is possible to charge the battery from a commercial power supply while preventing rotor rotation.
The afore-mentioned laid-open application further discloses a charging apparatus mounted on a vehicle including a sensor detecting a position of a magnetic pole of a rotor in the permanent magnet motor, means for selecting one-phase or two-phase coils that attain minimum torque for rotating the rotor based on the detected magnetic pole position of the rotor, and a control circuit charging the battery from a commercial power supply by causing a current to flow through the selected coil.
In the charging apparatus mounted on a vehicle, only a small torque is generated and, because of friction resistance of the vehicle and the like, rotor rotation is prevented. Therefore, by the charging apparatus mounted on a vehicle, movement of the vehicle during charging can be prevented.
When equal currents are caused to flow through three-phase coils of the motor, however, what can be utilized is only the leakage inductance of the coil. Therefore, there may be problems that the commercial power supply cannot sufficiently be boosted to the battery voltage, or influence of ripple to the input side increases.
Further, when the one-phase coil or two-phase coils are selected and a current is caused to flow therein, the motor generates torque and, possibility of the vehicle moving during charging cannot perfectly be eliminated.